Poured gypsum roof structure with lower vent means for removing excess moisture



March 3, 1970 p. A, g u ETAL 3,498,015

POURED GYPSUM ROOF STRUCTURE WITH LOWER VENT MEANS FOR REMOVING EXCESS MOISTURE Filed Nov. 15, 1966 2 Sheets-Sheet 1 I NV E N TORS Haul A. Seaburg Dona/d4. Green James M. Gal/away March 3, 1970 Filed Nov. 15, 1966 TOTAL WEIGHT LOSS POUNDS P. A. SEA'BURG ETAL 3,498,015

POURED GYPSUM ROOF STRUCTURE WITH LOWER VENT MEANS FOR l I l l l I o 5 I5 20 25 so 45 so 15 TIME AFTER POURING WEEKS INVENTORS Pau/A, Seaburg Dona/aAGreen JamesM Gal/away United States Patent 3,498,015 POURED GYPSUM ROOF STRUCTURE WITH LOWER VENT MEANS FOR REMOVING EXCESS MOISTURE Paul A. Seaburg, 11621 N. Bobolink Lane 30 W., Mequon, Wis. 53092; Donald A. Green, 3460 Catherine Drive, Allentown, Pa. 18103; and James M. Galloway, 1131 Kimberly Road, Bethlehem, Pa. 18018 Filed Nov. 15, 1966, Ser. No. 594,502 Int. Cl. E04b 1/16; E04c 2/24, 5/04 US. Cl. 52-310 8 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a roof construction and more particularly to backing sheets and a method of using such sheets as permanent forms for constructing roof slabs of settable cementitious material.

A roof for a commercial or industrial building is commonly constructed by fastening a plurality of rectangular backing sheets to the tops of horizontal supporting girders such as joists or purlins. Several inches of a settable cementitious mixture are then poured on top of the backing sheets and the mixture is left to set and harden. After a period of time ranging from a few minutes to several days depending on the type of mixture used, the slab will have hardened sufficiently to permit walking on the surface thereof for the installation of a waterproof wearing surface. The wearing surface placed on top of such slabs is usually the well-known built-up type of roofing membrane comprising layers of builders felt and hot asphalt with a final topping of gravel.

The installation of the waterproof wearing surface must often be delayed until the excess moisture in the slab has had an opportunity to evaporate if the sheets are made of a non-porous material such as metal. Otherwise, this moisture remains trapped between the impervious backing sheets and the waterproof wearing surface where it may cause blistering of the membrane, corrosion in the case of metal backing sheets or deterioration of the slab.

Mixtures containing gypsum are often preferred by some contractors for roof slabs because gypsum sets within a few minutes to form a slab hard enough to walk upon, thereby permitting in many cases, the waterproof wearing surface to be laid the same day that the slab is poured. Such gypsum mixtures usually contain considerable excess moisture that continues to evaporate from the slab long after the slab has taken its ini ial set. For this reason prior to our invention, contractors could only use gypsum mixtures with porous backing sheets of fiberboard or smiliar material through which the excess moisture could pass into the atmosphere below. The porous low strength backing sheets require a dense high strength gypsum mixture and also require special precautions to prevent them from being a safetv hazard du i g the construction of the roof due to their light weight and inability to support the weight of a workman.

It is therefore an object of our invention to provide a roof construction having a high strength backing sheet with a built-in venting feature for removing excess moisture from a roof slab.

It is a further object of our invention to provide a backing sheet for supporting, strengthening and receiving a settable cementitious material which is capable of removing excess moisture from the cementitious material after installation.

It is a still further object of our invention to provide a method of using backing sheets for constructing roof slabs from cementitious mixtures.

The foregoing objects, and other objects, and the means whereby they are accomplished pursuant to this invention can be attained by using a backing sheet of metal or other high strength material having a series of apertures with a thin layer of wicking material covering the apertures and bonded to the upper surface of the sheet, in the manner more particularly described below.

FIGURE 1 is a perspective view, partially in section, of a roof constructed according to our invention.

FIGURE 2 is a graph illustrating the effect on the drying rate of a roof slab using a corrugated metal backing sheet according to our invention.

Referring to FIGURE 1, horizontal girders 1 may consist of open-web joists as shown or any other suitable structural members, spaced at proper intervals. The backing sheets 2 are supported by and secured to girders 1 by self-tapping screws, clips or by welding. The sheets 2 are preferably corrugated and made of galvanized steel for high strength and long life since they remain as a permanent part of the roof structure. Adjacent sheets usually overlap one another slightly at the ends and the sides. The corrugated backing sheets 2 are usually placed so that corrugations are perpendicular to the girders 1 and overlap each other at the ends directly over a supporting girder 1.

The valleys 3 of the corrugated metal sheets 2 are provided with a series of apertures 4 punched or otherwise formed therein during the manufacture of the sheet. While we have illustrated a single row of relatively large diameter round apertures 4 in each valley, o her arrangements are possible according to this invention provided the total area of the openings is sufiicient to remove the excess moisture trapped in the overlying slab.

A thin layer of absorbent wicking material 5 such as a highly absorbent paper, fabric or felt, is bonded to the top surface of the corrugated metal sheet 2 with an adhesive 6 and covers the apertures 4. The wicking 5 is preferably cemented to the sheet 2 during the manufacture of the sheet with the adhesive 6 applied directly to the metal sheet rather than to the wicking to avoid sealing the surface of the wicking where it covers the apertures 4. We prefer to lay individual strips of the wicking 5 in the valleys 3 of the sheet rather than covering the entire sheet, for reasons of economy and ease of installation. Tests, using a gypsum mixture, have shown that there is little difference in drying rates between the two arrangements.

Once the backing sheets 2 are in place a layer of settable cementitious material 7 such as a gypsum mixture or a low density concrete is poured on top of the metal backing sheets 2 and the wicking 5. This layer is usually thick enough to provide an insulating cover above the crests of the corrugated sheets and usually averages from 2 to 4 inches in depth, measured to the bottom of the valleys. The top surface of the mix is screeded to form a smooth surface and then left to set and harden. After a period of time ranging from a few minutes for a gypsum mixture to several days for other mixtures, the resulting slab 7 has hardened sufliciently to permit walking on the surface thereof for the installation of the waterproof wearing surface 8, such as a built-up roofing membrane comprising alternate layers of roofing felt and hot asphalt with a final topping of gravel.

In the roof structure according to our invention the high strength corrugated metal sheet 2 acts as the structural supporting element and eliminates the need for any wire mesh reinforcing or sub-purlins as frequently had been required heretofore with low strength porous backing sheets. The number of apertures 4 in the sheets 2 are insufficient to appreciably affect the load carrying capac ity of the sheet. We have found that a single row of open ings /2 inch in diameter and 1 inch on centers in the valleys of the sheet and constituting approximately 6% of the surface area of the sheet provides a satisfactory drying rate for mixtures of settable cementitious mixtures containing considerable excess moisture such as gypsum mixtures.

The thin sheet of wicking covering the apertures 4 not only prevents the settable cementitious material from leaking through the apertures but also serves as a wick whereby excess moisture in the slab is drawn by capillary attraction to one of the apertures 4 where it is then dis sipated to the atmosphere. The wicking preferably ought to be capable of absorbing two or three or more times its own weight in Water in one hour. I have found an unsaturated builders felt 0.04 inch thick bonded to the top surface of the sheet 2 with a rubber base adhesive, provided the necessary wicking action to remove the excess moisture from the slab 7.

FIGURE 2 illustrates some of the results of a series of drying tests made over a 21 month period. The test specimens consisted of 2 inch thick slabs of a gypsum mixture poured over 16 inch by 3 inch galvanized steel forms. The gypsum mix for the specimens was proportioned one part water to one part gypsum by weight. Each specimen was poured in a mold which was removed immediately after the initial set of the gypsum. The entire specimen, excluding the apertures in the metal sheet, was wrapped in layers of metal foil, tape and then coated with paraffin. With this arrangement the excess moisture could escape only through the apertures in the metal sheet.

The specimens were allowed to dry at room temperatures and were weighed during the test at two week intervals with the weight loss indicating the amount of moisture lost during the interval between weighings.

In FIGURE 2, we have shown the test results of two specimens to illustrate the effect of the apertures and paper wicking on the drying rate of the specimens. Both specimens used a corrugated galvanized steel sheet having a single row of /2 inch diameter holes punched on 1 inch centers in the valleys giving a total open area of approximately 6.1% of the surface area of the sheet. Curve A illustrates the drying rate for the specimen using the perforated sheet without an overlying covering of wicking material. Curve B illustrates the drying rate of the specimen using the perforated sheet with an overlying covering of wicking material. It can easily be seen that a considerable increase in the drying rate is obtained by using the wicking material over the apertures in the corrugated metal backing sheet according to our invention.

While we have shown in the drawings a corrugated metal backing sheet having rounded crests, our invention can also be used with other high strength impervious materials such as fiberglass and certain plastics and with any of the other well known shapes for backing sheets such as corrugations of the channel-shaped or dove-tailed varieties.

We claim:

1. In a roof construction, in combination, a plurality of substantially rigid rectangular corrugated backing sheets, said sheets having a series of apertures formed therein, a layer of pliant wicking covering said apertures and bonded to the upper surface of said sheets in substantially full contact therewith, a layer of settable cementitious material on top of said sheets and said wicking and a waterproof wearing surface covering said cementitious material.

2. The roof construction of claim 1 wherein the backing sheets are metal and the apertures constitute approximately 6% of the surface area of the sheet.

3. The roof construction of claim 1 wherein the layer of wicking is in the form of elongated rectangular strips laid solely in the valleys of said rectangular corrugated backing sheets.

4. The roof construction of claim 1 wherein the layer of settable cementitious material is a mixture containing gypsum.

5. A method of constructing a roof comprising the steps of securing a plurality of substantially rigid corrugated sheets to the tops of horizontal roof girders, said sheets having a series of apertures formed in the valleys thereof and a layer of pliant wicking covering said apertures and bonded to the upper surface of said sheets in substantially full contact therewith, pouring a layer of settable cementitious material on top of said sheets and said wicking to fill said valleys and completely cover the crests of said sheets, allowing said cementitious material to set and harden, and covering cementitious material with a waterproof wearing surface.

6. A method of accelerating the drying of a settable cementitious material cast in situ on a corrugated sheet metal form comprising forming a plurality of apertures in the valleys of said sheet metal form, applying an adhesive to the top surface of said sheet metal form and covering said apertures and said adhesive with a layer of pliant wicking in substantially full contact with said top surface prior to the pouring of settable cementitious material on said form.

7. A backing for receiving and supporting settable cementitious material comprising a rectangular substantially rigid corrugated sheet having apertures formed therein and constituting approximately 6% of the sur face area of said sheet and a layer of pliant wicking bonded to and in substantially full contact with the upper surface of said sheet and covering said apertures.

8. A backing for receiving and supporting settable cementitious material comprising a substantially rigid corrugated rectangular metal sheet having apertures formed in the valleys thereof and a layer of pliant wicking bonded to and in substantially full contact with the upper surface of said sheet and covering said apertures.

References Cited UNITED STATES PATENTS Re. 26,141 1/1967 Hickman 52310 X 407,376 7/1889 Smith 52338 1,501,850 7/1924 Karstens et al. 52-662X 2,121,789 6/1938 Davey 52305 X 3,193,971 7/1965 Galloway 52336 X 3,203,146 8/1965 Carter 52-328 3,276,171 10/1966 Brown 52-336 X ALFRED C. PERHAM, Primary Examiner US. 01. X.R. 52-302, 328, 336, 66.2, 674, 74

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,498 ,015 March 3, 1970 Paul A. Seaburg et :11.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 8, the following words have been omitted I-)lass1gn0rs to Bethlehem Steel Corporation, a corporation of e aware Signed and sealed this 25th day of August 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLEIL JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer 

